Original paper

Korobitsynite from the Aris phonolites, Windhoek, Namibia

Niedermayr, G.; Gault, R.A.; Petersen, O.V.; Brandstä tter, F.

Abstract

The very rare mineral korobitsynite, first described from the Alluaiv and Karnasurt Mountains, Lovozero alkaline massif, Kola Peninsula, Russia, has been found recently at the Ariskop phonolite quarry, 25 kilometres S of Windhoek in central Namibia. The unit cell parameters of the Aris korobitsynite, obtained on a Bruker AXT four-circle-diffractometer, are a = 7.34(1), b = 14.12(1) and c = 7.11(3)Å and are in good agreement with the data given for the Kola material. The empirical formula of the korobitsynite from Aris, calculated from the microprobe analysis, assuming (Si,Al) = 4 and (O,OH) = 2, is: (Na2.32K0.01Ca0.01)Σ2.34(Ti1.21Nb0.75Zr0.01Ta0.01)Σ1.98(Si3.99Al0.01)4O12(O1.02OH0.98)2·3.75H2O. The korobitsynite from the Aris phonolites forms colourless and transparent, prismatic crystals up to 1mm in length, as individuals or in sprays scattered on a matrix of platy albite and analcime crusts. The crystals show {110} moderately dominating the prismatic habit, with minor {010} and {001} in addition. The korobitsynite from Aris is biaxial positive with 2Vmeas. = 28(0.5)°, nα = 1.6468(5), nβ = 1.6528(5) and nγ = 1.7593(5), and has α = b, β = c, γ = a. The optical properties of the Aris korobitsynite given are in excellent agreement with those of korobitsynite from the type locality.

Keywords

korobitsynitethe aris phonolites- namibia